Method for recycling pet bottle

ABSTRACT

A through process comprising depolymerization reaction of used PET bottles with EG, recovering DMT by ester interchange reaction with MeOH, obtaining terephthalic acid by hydrolysis of the recovered DMT, and manufacturing a PET polymer which can be used for manufacturing PET bottles again by using the terephthalic acid.

TECHNICAL FIELD

The present invention relates to a method for obtaining a polymer forPET bottle again from resin bottle wastes containing polyethyleneterephthalate (hereafter, this may be abbreviated as PET) as the maincomponent. More specifically, the invention relates to a method carriedout as follows: resin bottle wastes containing PET as the main componentand further containing components different from PET are subjected topretreatments of crushing, washing, removing foreign bodies etc.; theproduct is subjected to chemical reaction treatments to recover ahigh-purity dimethyl terephthalate (hereafter, this may be abbreviatedas DMT) as an effective component; terephthalic acid (hereafter, thismay be abbreviated as TA) is obtained through chemical reactions fromthe recovered DMT; and further the terephthalic acid is converted to aPET polymer for PET bottles.

BACKGROUND ART

A polyalkylene terephthalate, especially PET is manufactured and used inlarge quantities in the fields of living related materials such asfiber, film and resin, food related materials such as bottles fordrinking water and carbonated drinks, and others because of itsexcellent chemical stability.

However, the disposal of wastes of fiber, film and resin products, andoff-specification PETs, which are largely generated with increasingmanufacturing quantities and consumption quantities, is presentlybecoming large social issues. Regarding material recycling, chemicalrecycling, thermal recycling etc., various methods have been proposed.

On the other hand, although especially the disposal of PET, bottlesamong the wastes is becoming more serious due to bulkiness, onlymaterial recycling that recovered used PET bottles are remelted andfibers are produced from the molten matter, is realized as a recyclingmethod. But, when melt molding is simply used, it is not possible toreuse as PET bottles because of the deterioration of physicalproperties.

Further, a refilling method that PET bottles are washed and refilled hasissues regarding the following, that is, who paying the cost ofrecovery, the points of safety and hygiene, and limitation in the numberof times of reusing. The PET bottles are ultimately disposed, and themethod can not be an permanent countermeasure. Further, PET bottlewastes contain foreign resins represented by polystyrene (hereafter,this may be abbreviated as PS), polypropylene (hereafter, this may beabbreviated as PP) and polyethylene (hereafter, this may be abbreviatedas PE) which are originated from PET bottle product-constitutingmaterials, for example, labels, shrink films, base caps, caps or thelike, foreign plastics such as polyvinyl chloride (hereafter, this maybe abbreviated as PVC) and polyolefinic resins, aluminum derived fromcaps and aluminum cans, iron derived from steel cans, adhesives,pigments, dyes and others.

Even in a bale of PET bottles recovered through collection of classifiedrefuse, the mixing of foreign materials is hardly avoided. Even inchemical recycling that PET bottles are decomposed to monomersconstituting the PET polymer by using a solvent such as water, methanol(hereafter, this may be abbreviated as MeOH) or ethylene glycol(hereafter, this may be abbreviated as EG), and the monomers are reused,the foreign materials generate various decomposition gases (for example,hydrogen chloride gas etc.) and various decomposition products (forexample, lower hydrocarbons etc.) in the courses of heating process andreaction process, or mixed materials themselves sometimes largelydeteriorate the quality of the monomer (DMT) recovered by chemicalreactions, or they melt and become solid in recovering apparatuses todamage machinery and tools.

The chemical recycling includes, for example, a method by whichpolyester wastes are hydrolyzed in the presence of an alkali compound toobtain TA described in JP-A 11-21374 (JP-A means Japanese unexaminedpatent publication) and a method by which DMT and EG are obtained by gasphase MeOH decomposition in MeOH described in U.S. Pat. No. 5952520.

However, since these processes all need a reaction condition of hightemperature of 200° C. or higher, they have very low allowance againstthe mixing of foreign plastics which start to decompose from thetemperature of 190° C., for example, PVC and whose decomposed productscause quality deterioration of the final product.

Further, JP-A 2000-169623 describes a process in which PET wastes aredecomposed with EG, the recovered bis-β-hydroxyethyl terephthalate(hereafter, this may be abbreviated as BHET) is purified by a thin-filmevaporator, and subsequently the BHET is subjected to meltpolycondensation to obtain PET polymer. However, this process also has astep imposing a heat history of 200° C. or higher, and the allowance ofmixing of heat-decomposable foreign plastics such as PVC is small.

Namely, although chemical recycling has an allowance of the mixing ofimpurities larger than that of material recycling, it is required toremove the impurities almost completely in pretreatment processes.Further, it is generally known that the PET polymer for bottles ismanufactured by obtaining an oligomer through an ester interchangereaction or an esterification reaction of DMT or TA used as a startingmaterial with EG followed by a polycondensation reaction which iscarried out successively. In this case, the DMT or TA of the rawmaterial should be highly purified, and the contents of impuritiesshould be sufficiently little; and otherwise, the obtained PET polymercan not be used for PET bottles.

Due to the circumstances having above mentioned various restrictions, noprocess capable of recovering effective components from used PET bottlesthrough a chemical recycling process and again obtaining a PET polymerusable for PET bottles has been reported.

DISCLOSURE OF THE INVENTION

The object of the present invention is to solve the above-mentionedproblems of the conventional technologies and to propose a process that,even from used PET bottles containing impurities, a pollution-freehigh-purity monomer (DMT) can be obtained, and a PET polymer suitablefor PET bottles can be manufactured effectively from the high-purityDMT.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an outline drawing schematically exhibiting one mode of themethod for recycling PET bottles in the present invention, forexplaining the flow of the processes.

BEST MODE FOR CARRYING OUT THE INVENTION

The method of the present invention, that is, a high-purity DMT isrecovered as an effective component from wastes of resin bottlescontaining PET as the main component and further containing componentsdifferent from it, TA is obtained through chemical reactions, andfurther a PET polymer for PET bottles is obtained, is characterized inthat the resin bottle wastes are treated in such a manner that thefollowing Processes (1) to (17) are passed sequentially.

-   (1) A process for unpacking a packed bale of PET bottles which have    been recovered through collection of classified refuse.-   (2) A process for removing iron and aluminum by a metal detector    from the unpacked PET bottles, and subsequently crushing the PET    bottles into flakes of 2-30 mm in sizes.-   (3) A process for separating polymer components different from PET,    of labels (thin film) and consisting of PE, PS, PVC or the like from    flaky pieces of PET bottles by winnowing.-   (4) A process for washing and gravity sorting which has both the    roles of washing out foreign materials attached inside and outside    the crushed bottle pieces and/or residues of the contents inside the    PET bottles with water, and further removing sands and stones having    specific gravities larger than water and PET, and foreign plastics    such as PE and PP having specific gravity smaller than water.-   (5) A depolymerization process for producing BHET by charging    recovered PET flakes into EG containing a PET depolymerization    catalyst and treating the mixture at 175-190° C. under a pressure of    0.1-0.5 MPa.-   (6) A solid-liquid separation process for removing solid foreign    materials which have not dissolved in the above reaction solution.-   (7) A BHET concentration process for distilling and concentrating    the solution fraction which has passed the solid-liquid separation    process.-   (8) An ester interchange-recrystallization process for forming crude    DMT and EG through an ester interchange reaction of the concentrated    BHET in MeOH in the presence of an ester interchange reaction    catalyst, and subjecting the reaction mixture to recrystallization    in a MeOH solvent.-   (9) A DMT distillation process for removing MeOH by distillation    from the DMT cakes to purify the DMT.-   (10) A hydrolysis process for subjecting the purified DMT obtained    in the DMT distillation process to a hydrolysis reaction together    with water at 230-250° C. to produce TA.-   (11) A process for cooling an aqueous slurry of the TA obtained in    the hydrolysis process.-   (12) A process for obtaining TA cakes from the cooled aqueous slurry    of TA through solid-liquid separation.-   (13) A slurry adjusting process for mixing the TA cakes with EG, and    adjusting the mole ratio of TA/EG to 1:1to 1:3.-   (14) A process in which TA and EG are made to perform an    esterification reaction to obtain a PET oligomer.-   (15) An initial melt-polycondensation process in which a    polycondensation catalyst and a stabilizer are added to the PET    oligomer, the mixture is subjected to a melt polycondensation    reaction in a weak vacuum of 1.3 kPa to 4.0 kPa at 260-300° C. to    remove EG, and thus the degree of polymerization is increased.-   (16) A latter term melt-polycondensation process in which the    product of the previous process is further subjected to a melt    polycondensation in a high vacuum of 67 Pa to 0.7 kPa at 270-300° C.    to remove EG by distillation, and thus the degree of polymerization    is further increased.-   (17) A solid phase polymerization process for increasing the degree    of polymerization in order to obtain a PET suitable for bottles.

Hereafter, the present invention will be explained process by process.In the present invention, Processes (1) to (4), which precedes theprocesses accompanied by chemical reactions, are called pretreatmentprocesses. In the pretreatment processes, a packed bale of PET bottleswhich have been recovered through collection of classified refuse isunpacked, and subsequently, iron and aluminum are removed. These metalscan be easily removed by using a metal detector. Subsequently, therecovered PET bottles are crushed into pieces of 2-30 mm in sizes. Thesizes of crushed pieces are more preferably 2-20 mm. By this treatment,the depolymerization reactivity is improved, and the performance fortreating PET bottle wastes is increased. This effect is especiallysignificant for the thick parts which have been treated forcrystallization and whitening in order to increase the strength andstabilize the size of PET bottles. The crushed products often containforeign plastics different from polyester such as PE, PP, PS and PVC,which are materials of caps or labels contained in the polyester resinas impurities.

In the present invention, to cope with the mixing of the above-mentionedforeign plastics, reaction conditions are selected so that they aredecomposed in the later reaction processes, and the purity of therecovered monomer is not lowered; however, there remains such apossibility that the foreign plastics have undesirable influences onhandling, for example, they may stick on reactors, cause clogging on afilter and so on. Accordingly, to promote the reactions smoothly, it isimportant to remove the foreign plastics in the pretreatment processes,and suppress their mixing into the reaction processes as far aspossible.

However, it is not necessary for the present invention to includevarious processes to completely remove the above-mentioned foreignplastics, which is the case of material recycling, but only processes ofnecessity minimum are required.

In order to remove thin films (PE, PP, PS, PVC etc.) used in labels etc.and different than polyester, from the above crushed products, at first,winnowing is used to remove labels. When the air volume is too large,the useful component of polyester resin is removed together, andaccordingly the air volume should be controlled. By the winnowing,labels mainly comprising PP, PS or PVC can be removed almost completely.

Subsequently, in order to remove caps composed mainly of PE, which cannot be removed by winnowing, the crushed material is treated by agravity sorter. The foreign plastics such as PP and PE having a specificgravity lighter than water are removed by the gravity sorting to obtainrecovered flakes.

Since the above-mentioned gravity sorter works also as an apparatus forwashing out the impurities originated from foods (refreshing drink, soysauce or the like) attached and remained on polyester resin or the likewith water, there is no problems even in the case where contents remaininside the resin. The wash water separated by a centrifuge is recycledto the gravity sorter again, and a part is purged and treated as wastes.Further, sands and stones having specific gravity extremely larger thanthe specific gravities of water and PET are removed by the sedimentationon the bottom of the water washing machine.

The recovered flakes which have been discharged from the gravity sorterare transported by pneumatic transportation to a reactor in a reactionprocess via a flake storing tank. In the case where the sizes of theflakes after crushing are specified at a relatively large range of30-150 mm in the above-mentioned crushing process, the transportationefficiency in the pneumatic transportation process becomes poor, andproblems of the clogging of a rotary valve and the like may occur, andaccordingly, it is effective to crush to about 2-30 mm in sizes like thepresent invention.

Further, on the recovered flakes before the pneumatic transportation,the water used in centrifugal operation with a decanter remains in anamount of about 0.5 wt. % based on the weight of the recovered flakes.Water exerts unfavorable influences on the reaction velocity in thedepolymerization process, but the remaining water is dried during thepneumatic transportation, and the water content is lowered down to 0.1wt. % or less based on the weight of the recovered flakes finally, andthereby there is no problem in the progress of the reaction.

In the above-mentioned pretreatment processes, most of the componentsother than polyester can be removed, that is, the pretreatment iscompleted with widely smaller number of processes than in the case ofmaterial recycling. This is because that, if impurities remain, they canbe removed in the later processes through physical and chemicalseparation methods. Further, in the material recycling, colored bottlesbecome impurity, and they must be removed by a sorter, but in the methodof the present invention, the pigments contained in the colored bottlesalso can be removed in later reaction processes, and the bottles can berecycled as useful resource.

Next, the depolymerization catalyst to be used in Process (5) containsat least one kind of metal compound selected from a group consisting ofcarbonate salts, hydrogencarbonate salts, hydroxides and alkoxides of analkali metal, carbonate salts, hydrogencarbonate salts, hydroxides andalkoxides of an alkaline earth metal, manganese acetate and zincacetate, and the quantity of the addition of the catalyst is preferably0.1 to 10 wt. % based on the weight of the PET flakes supplied toProcess (5). Further, the quantity of EG to be used in Process (5) ispreferably 0.5 to 20 times the quantity of the PET flakes supplied toProcess (5) by weight. The reaction is preferably carried out underreaction conditions of a temperature of 175 to 190° C., and a pressureof 0.1 to 0.5 MPa. Thus, BHET is obtained.

Further, in Process (6), the solid foreign materials which did notdissolve in the reaction solution is removed by a solid-liquidseparation.

In Process (7), the water component in the crude BHET generated as aby-product in the depolymerization reaction is mainly removed bydistillation. In the process, the distillation-condensation operation iscarried out preferably under a pressure of 1.3 to 133 kPa.

The ester interchange reaction catalyst to be used in Process (8)contains at least one kind of metal compound selected from a groupconsisting of carbonate salts, hydrogencarbonate salts, hydroxides andalkoxides of an alkali metal, carbonate salts, hydrogencarbonate salts,hydroxides and alkoxides of an alkaline earth metal, manganese acetateand zinc acetate, and the quantity of the addition of the catalyst ispreferably 0.1 to 10 wt. % based on the weight of the PET flakessupplied to Process (5). Further, the quantity of MeOH to be used inProcess (8) is preferably 0.5 to 20 times the quantity of the PET flakessupplied to Process (5) by weight. The reaction is preferably carriedout under reaction conditions of a temperature of 65 to 85° C., and apressure of 0,1 to 0.3 MPa.

In Process (9), mainly MeOH is distilled out from the obtained DMT caketo purify the DMT.

In Process (10), water is supplied in an amount of 0.5 to 5 times,preferably 0.8 to 1.2 times the weight of the DMT, and the reaction iscarried out preferably at a temperature of 230 to 270° C.

An aqueous slurry of the TA which is obtained by cooling the reactionmixture of the above process is prepared in Process (11); and the slurryis subjected to a solid-liquid separation process for dehydration, and awater-containing TA cake having a water content of preferably about 10to 20 wt. % is separated and recovered in Process (12).

EG is added to the obtained water-containing TA cake in such a mannerthat the molar ratio of TA/EG becomes 1:1 to 1:3 to prepare a slurry inProcess (13). The content of water in the slurry is preferably in therange of 0,1 to 20 wt. % based on the weight of EG.

In stead of the above Process (13), the following Processes (13a) to(13b) may be passed before advancing to Process (14).

Process (13a): the TA cake obtained in Process (12) is treated by adryer such as a vibrating fluid bed-type dryer or an inert gas flow-typedryer to obtain TA powder having water content of 0.5 wt. % or less.

Process (13b): the TA powder obtained in Process (13a) is placed into aslurry preparation tank, EG is charged so that the molar ratio of TA/EGbecomes 1:1 to 1:3, and thus, a slurry is prepared.

But, in the case of passing through Processes (13a) and (13b), a largequantity of energy is consumed to dry the water in the TA cake, andaccordingly, the mode passing Process (13) is better than that passingProcesses (13a) and (13b).

Further, it is preferable that the TA obtained through the hydrolysis ofDMT is slurried in EG in a state where a small amount of water remainsin it because this increases handleability. The water content in the EGslurry of TA is preferably in the range of 0,1 to 20 wt. % based on theweight of EG, especially preferably 1 to 5 wt. %.

In Process (14), when TA and EG are subjected to an esterificationreaction to obtain a PET oligomer, the esterification temperature ispreferably 260 to 270° C.

In Process (15), the polycondensation reaction catalyst to be added tothe PET oligomer is selected from a group consisting of germanium,antimony and titanium compounds represented by germanium oxide, antimonytrioxide and titanium trimellitate, and the addition quantity ispreferably 0.002 to 0,1 wt. % based on the weight of TA supplied toProcess (13). Further, a stabilizer to be added is preferably aphosphoric ester such as trimethyl phosphate, triethyl phosphate ortriphenyl phosphate, a phosphorous ester such as triphenyl phosphite ortrisdodecyl phosphite, an acidic phosphoric ester such as methyl acidphosphate, dibutyl phosphate or monobutyl phosphate, or a phosphoruscompound such as phosphoric acid, phosphorous acid, hypophosphorous acidor polyphosphoric acid. The reaction conditions are preferably atemperature of 260 to 300° C. and a weak vacuum of 1.3 kPa to 4.0 kPa.

In Process (16), the reaction conditions are preferably a temperature of270 to 300° C. and a strong vacuum of 67 Pa to 0.7 kPa.

In Process (17), the solid phase polymerization reaction, which adjuststhe degree of polymerization and decreases the content of cyclicoligomers, acetaldehyde etc., may be carried out either in a nitrogenstream or in a vacuum.

Hereafter, the present invention will be explained further in detail byusing FIG. 1, which shows one mode of the method of recycling of PETbottles in the present invention.

Recovered PET bottle flakes which have been treated in the pretreatmentprocesses (not shown in the figure) of Processes (1) to (5), adepolymerization reaction catalyst and further EG are chargedconcurrently into a depolymerization tank (1 in the figure) from asupply source (11 in the figure), a supply tank (10 in the figure) and asupply line (10a in the figure), respectively, and the PET flakes aredepolymerized in the depolymerization tank (1 in the figure).

The depolymerized mixture is sent to a solid-liquid separation apparatus(2 in the figure). The components which do not dissolve in thedepolymerization tank (1 in the figure) are separated by thesolid-liquid separation apparatus (2 in the figure), and they areremoved outside the system as solid materials. The solid materials arefurther washed with EG in a washing tank (3 in the figure), and thematerials attached on the solid materials are recycled to thedepolymerization tank (1 in the figure) if required. The solid materialsthemselves are removed into a solid material tank (16b in the figure)separately. Preferably, the retention time in the depolymerization tank(1 in the figure) is 1 to 10 hr, and the inner temperature is 175 to190° C.

Subsequently, the depolymerization reaction product after the completionof the depolymerization is sent to a distillation-concentration tank (4in the figure), and EG is removed by distillation so that the ratio ofEG to the depolymerization reaction product becomes 0.5 to 2.0 in termsof a charged weight ratio in the next process. The removed EG can berecycled to the depolymerization tank (1 in the figure).

Subsequently, the concentrated liquid of the depolymerization reactionproduct is fed to an ester interchange reaction tank (5 in the figure),and an ester interchange reaction catalyst and MeOH are-fed from anester interchange reaction catalyst supply source (13 in the figure) anda MeOH supply source (12 in the figure), respectively. Thus, thedepolymerization reaction product is converted to DMT and EG. It ispreferable to carry out the reaction in the ester interchange tank atthe inner temperature of 65 to 85° C., the inner pressure of 0,1 to 0.3MPa and the retention time of 0.5 to 5 hr. After adding an excess amountof MeOH, the obtained mixture of DMT and EG is cooled, and the mixtureis treated by a solid-liquid separation apparatus (6 in the figure) toproduce DMT cakes, and a mixture of EG and MeOH.

Since the separated DMT cakes contain MeOH as a mother liquid, they areslurried again in MeOH, and subjected to solid-liquid separation.Further, the DMT cakes are supplied to a DMT distillation tower (7 inthe figure), and the purified DMT is collected in a DMT recovery tank(14 in the figure). A part of the residual liquid on the bottom of thedistillation tower (7 in the figure) is returned to the depolymerizationtank (1 in the figure) through a line (7a in the figure), and the restis disposed to the outside (18 in the figure) of the system.

On the other hand, the mixed liquid of EG and MeOH obtained by thesolid-liquid separation is supplied to a MeOH rectification tower (9 inthe figure), and MeOH is distilled out. The distilled-out MeOH can beused as a part of the MeOH which is supplied to the ester interchangereaction tank (5 in the figure). Further, the residual liquid on thebottom of the MeOH rectification tower (9 in the figure) is supplied toan EG distillation tower (8 in the figure) to distill out EG. A part ofthe distilled-out EG is recycled as the EG supplied to thedepolymerization tank (1 in the figure) through the line (10a in thefigure), and the excess EG is collected and taken out to the outside (15in the figure) of the system.

Furthermore, a part of the residual EG of the EG distillation tower (8in the figure) is returned to the depolymerization tank (1 in thefigure) and the rest is taken out to the outside (17 in the figure) ofthe system as a waste.

Continuously, the process for obtaining TA by subjecting the DMT to ahydrolysis reaction will be explained by using FIG. 1.

The DMT which has been purified and is stored in the DMT recovery tank(14 in the figure) is heated up as in a molten state to the hydrolysisreaction temperature in a DMT heater (19 in the figure). The heated DMTis supplied to a hydrolysis reaction tank (20 in the figure) togetherwith hot water which has been heated in a water boiler (28 in thefigure). The weight ratio of the water/DMT supplied to the reaction tankis preferably in the range of 1:0.5 to 1:4. The reaction temperature andthe reaction pressure in the reaction tank are preferably 230 to 250°C., and 2.9 to 4.0 MPa (gauge pressure), respectively. The hydrolysisreaction is an equilibrium reaction, and a high reaction rate can berealized by effectively removing the byproduced MeOH in the reaction.Accordingly, as a heat source for quickly removing the MeOH and keepingthe reaction temperature, high-pressure steam generated in the waterboiler (28 in the figure) is introduced into the reaction vessel. TheMeOH byproduced in the hydrolysis reaction and the entrained water areremoved from the upper part of the reaction tank. It is preferable thatthe weight of the steam introduced from the water boiler is equal tothat of the water taken out from the upper part of the reaction tank.The retention time in the hydrolysis reaction tank is preferably 1 to 5hr.

Next, the hot TA/water slurry obtained in the hydrolysis reaction tank(20 in the figure) is supplied to a cooling tank (21 in the figure) forcooling it. In the cooling tank, the slurry receives quick pressurechange, and the water in the slurry is vaporized. In order to make upfor the deficiency of water due to the vaporization and its consumptionby the reaction, water is supplied from a water supply tank (29 in thefigure). The water to be supplied is preferably ion-exchanged pure waterin order to prevent the contamination of the product by impurities.Further, it is preferable to use the water whose dissolved air,especially oxygen has been removed in order to prevent the erosion ofequipments including the hydrolysis reaction tank.

The cooled TA/water slurry is supplied to a solid-liquid separator (22in the figure), and it is separated into TA cakes and water. The TAcakes obtained by the solid-liquid separator are supplied to a slurrypreparation tank, and a slurry having a molar ratio (EG/TA) of 1:1 to1:3 is prepared with EG supplied from an EG supply source (25 in thefigure).

The mixed vapor of water/MeOH generated from the hydrolysis reactiontank (20 in the figure) is condensed by a steam condenser (26 in thefigure), subsequently it is separated by distillation to MeOH and waterwith a MeOH distillation tower (27 in the figure), the MeOH obtainedfrom the top of the distillation tower is supplied to theabove-mentioned MeOH rectification tower (9 in the figure), and it istreated by distillation again. Further, the water obtained from thebottom of the MeOH distillation tower (27 in the figure) is sent to awater supply tank (23 in the figure), heated in the water boiler (28 inthe figure) and recycled to the hydrolysis reaction tank (20 in thefigure) again.

A part of the MeOH byproduced in the hydrolysis reaction becomesdimethyl ether (hereafter, this may be abbreviated as DME) throughdehydration reaction. The DME is sent to a waste gas treating apparatus(30 in the figure) from a steam condenser (26 in the figure) in gas asit is and subjected to incineration disposal.

Further, the water separated by the solid-liquid separator (22 in thefigure) is mostly sent to the water supply tank (23 in the figure) torecycle and partly sent to a waste-water treatment facility (32 in thefigure) as waste water.

Successively, the processes for obtaining a PET polymer from theobtained TA slurry will be explained by using FIG. 1.

The TA/EG slurry whose mole ratio has been adjusted in a TA slurry tank(24 in the figure) is supplied to an esterification tank (33 in thefigure), and a PET oligomer is obtained through an esterificationreaction. Preferably, the reaction temperature of the esterificationtank (33 in the figure) is 260 to 270° C. and the retention time is 1 to5 hr.

During the reaction, the reaction product mixture of EG/water isdistilled out, and the distillate is separated to EG and water by an EGdistillation tower (41 in the figure). The EG is redistilled by an EGdistillation tower (30 in the figure), and further redistilled by the EGdistillation tower (8 in the figure).

The PET oligomer obtained in the esterification tank (33 in the figure)is supplied to an initial polycondensation reaction tank (34 in thefigure) after the addition of germanium dioxide as a catalyst andtrimethyl phosphate as a stabilizer, and a polycondensation reaction iscarried out under conditions of a weak vacuum of 1.3 to 4.0 kPagenerated by a vacuum apparatus (44 in the figure) and a temperature of260-300° C. Further, the obtained initial polycondensation product issupplied to a latter-term polycondensation reaction tank (35 in thefigure), and a polycondensation reaction is carried out in a high vacuumof 67 Pa to 0.7 kPa generated by the vacuum apparatus (44 in the figure)at 270 to 300° C. Both the EG fractions byproduced in polycondensationreactions in the initial polycondensation reaction tank (34 in thefigure) and the latter-term polycondensation reaction tank (35 in thefigure) are subjected to distillation treatments in the EG distillationtower (8 in the figure) via the EG tank (30 in the figure).

The PET polymer obtained in the latter-term polycondensation reactiontank (35 in the figure) is taken out from it in a plate or strand, andcooled in a cooling bath (36 in the figure). Then, it is cut by a cutter(37 in the figure) into pellets. In order to adjust the degree ofpolycondensation of the PET polymer at the specific level suitable forPET bottle, the obtained PET pellets are treated for a polycondensationreaction in a pellet state in a solid phase polymerization tank (38 inthe figure) furnished with a dryer and a preliminary crystallizer. Thepolycondensation reaction can be carried out either in a vacuum or innitrogen stream. The final PET product is stored in a storage tank (39in the figure). The PET polymer is used as a polymer suitable for PETbottles.

Further, the wastes of PET oligomers and PET polymers which aregenerated from the initial polymerization tank, the latter-termpolymerization tank and the solid-phase polymerization tank, can besupplied directly to the depolymerization reaction tank to depolymerizethem, or they are supplied to a crusher, and after crushing, they aresupplied to the depolymerization reaction tank, depending on theirforms. Thus, the losses of wastes in a series of the processes can bemade as little as possible, and the wastes can be recycled. Further,considerable parts of the water, EG and MeOH generated in every processcan be recycled to any process in a series of the processes bysubjecting them to a distillation treatment in advance. Accordingly, thewastes can be recycled with the loss suppressed as far as possible.

EXAMPLES

The present invention will be explained further in detail hereafter withexamples, while the present invention is not restricted by the examples.Further, each value in the examples was obtained in accordance with thefollowing methods.

1. Analysis of DMT (1)

(1) Chlorine Content in DMT

A DMT sample was dissolved in MeOH, and the chlorine concentration wasdetermined by using a chlorine-sulfur analyzer/-total-organic halogenanalyzer (“TOX 100” manufactured by Mitusi Chemical) on the basis of themixture whose chlorine content had been determined in advance.

(2) Organic Impurities in DMT

A DMT sample was subjected to recrystallization treatments by using anacetone solvent and a MeOH solvent, and the collected solvents wereconcentrated. The impurities in the concentrate were determined by gaschromatography (instrument: HP 5890 manufactured by Hewlett-Packard;capillary column: DB-17 manufactured by J&W) using an acetone solvent ofa guaranteed grade as the sample solvent.

2. Analysis of Terephthalic Acid

(3) 4-CBA and p-TA

A TA sample was dissolved in 2N-ammonia water, and 4-CBA and p-TA wereseparately determined on a liquid chromatograph system (LC-6Amanufacturing by Shimazu) with STR Φ DS-H column.

(4) Weight Concentration of MMT and DMT

These were determined by high-speed liquid chromatography (instrument:HPLC D-7000 manufactured by Hitachi; filled column: RP-18, 2 pieces).

(5) Weight Concentration of BA

A TA sample was esterified with diazomethane, and the esterified samplewas analyzed on a gas chromatograph using a separation column of 10%SE-30 with an inner standard of n-tridecane.

(6) 250° C. Heat-resistant Alkali Permeability

After held for 2 hr at 250° C., a TA sample was dissolved in a2N-potassium hydroxide solution, and the UV-permeability of the solutionat 400 nm in wave length was determined by a spectrophotometer (aninstrument equivalent to UVIDEC 660 manufactured by Nippon Bunkou).

3. Analysis of PET

(7) Intrinsic Viscosity

According to a conventional method, a sample was taken out from a chipor a molded body, a certain amount of the sample was weighed out, it wasdissolved in o-chlorophenol so that it became 0.012 g/ml inconcentration, the viscosity of the solution was determined with anOstwald viscometer at 35° C. after the solution was once cooled, and theintrinsic viscosity was calculated from the viscosity.

(8) Haze

A sample was cut out in a size of 50 mm×50 mm from the body part of aPET bottle. Haze was determined on the sample by using a color and colordifference meter (MODEL 1001 DP) manufactured by Nippon Denshoku.

(9) Content of Acetaldehyde

The content of acetaldehyde (hereafter, this is abbreviated as AA) wasdetermined by freezing and crushing a sample, charging the crushedproduct into a vial, holding it for 60 min at 150° C., and analyzing thegas in the vial by using a head-space gas chromatograph manufactured byHitachi.

(10) Content of Diethylene Glycol

A sample was decomposed with hydrazine hydrate and analyzed by a gaschromatograph (“263-70” manufactured by Hitachi).

(11) Content of Oligomer (Cyclic Trimer)

A sample was crushed with a crusher, a certain amount of the crushedproduct was weighed out, it was once dissolved in a small amount of amixed solvent of hexafluoroisopropanone/chloroform, and subsequently thesolution was diluted to a certain concentration (50 g/L) withchloroform. On this sample solution, a low molecular weight region wasfractionated by gel permeation chromatography (GPC; ALC/GPC 244manufactured by Waters), the corresponding peak was detected, and theamount of the oligomers in the sample was determined by using the peakbased on a calibration curve prepared from a standard sample of thecyclic trimer.

Example 1

A bale (900 mm×1,000 mm×550 mm, and 120 kg) of PET bottles which hadbeen recovered through collection of classified refuse was unpacked,iron and aluminum were removed by a metal detector, subsequently thematerials were charged into a crusher, and a crushing operation wascarried out with a screen whose aperture was set 10 mm. The crushedproduct was treated by a winnower to remove labels composed mainly ofPE, PS and PP attached on bottles, subsequently, it was subjected to awashing-gravity separation process to washing out the content of bottlesand at the same time to remove caps composed mainly of PP and PE, andthe labels which was not removed by the winnowing, and thus, PET flakeswere recovered. The recovered PET flakes were transported by pneumatictransportation to a recovered PET flake-supplying tank in order to storethem in the tank. Subsequently, 100 pts. wt. of the recovered PETflakes, 360 pts. wt. of EG and further 2.7 pts. wt. of sodium carbonatewere supplied to a depolymerization tank from the recovered PETflake-supplying tank, a EG supply line and a polymerization catalystsupplying tank, respectively. They were held for 4.5 hr at 180° C. understirring.

The resulting solution of the depolymerization reaction with EG wascharged into a filter having the periphery surrounded with heating unitsheated at 170° C. and furnished with a 100-mesh metal net as a filtermedium, and filtered at a high temperature. The remaining materials onthe filter medium was washed with 90 pts. wt. of EG heated at 170° C.,and the washing was pooled in a washing reservoir.

The depolymerization reaction treatment solution obtained by the hotfiltration was concentrated by reduced pressure distillation at 6.65kPa, and 270 pts. wt. of EG was recovered as a distillate.

The resulting concentrate, and 2.7 pts. wt. of sodium carbonate from anester interchange catalyst tank and further 180 pts. wt. of MeOH werecharged into an ester interchange reaction tank, and they were held at aliquid temperature of 74° C. under normal pressure for 1 hr understirring to carry out an ester interchange reaction. The resultingmixture of DMT, EG and MeOH was cooled to 40° C., and successivelytreated with a solid-liquid separator to obtain DMT cakes. The DMT cakeswere once placed in a MeOH washing tank, 180 pts. wt. of MeOH wascharged into it, the mixture was stirred at 40° C. to wash the DMT, themixture was treated by the centrifugal separator to separate the solidportion from the liquid portion, and DMT cakes were again obtained. Theobtained DMT cakes were again placed in the MeOH washing tank, and theDMT cakes were melted at 160° C. this time, and at the same time theresidual MeOH was distilled out. The molten DMT was charged into a DMTdistillation tower, DMT was distilled out as a distillate by a reducedpressure distillation at a pressure of 6.65 kPa to obtain 83 pts. wt. ofa recovered DMT. The molten DMT was sent to a DMT recovery tank.

The DMT recovered by the process was a high purity DMT having a chlorineconcentration of 1 ppm or less and a total amount of organic impuritiesof 100 ppm or less.

Subsequently, to a hydrolysis reaction tank were each continuouslysupplied the molten DMT from the DMT recovery tank at a speed of 100pts. wt./hr, hot water from a water boiler at a speed of 100 pts. wt./hrand further high-pressure steam form the water boiler at 270° C. at aspeed of 40 pts. wt./hr, respectively. The hydrolysis reaction wascarried out under stirring by keeping the liquid temperature of thehydrolysis reaction tank at 250° C. and a retention time of 4 hr. TheMeOH generated in the reaction was distilled out from the head of thereaction tank together with steam. The speed of the distillation was atabout 400 pts. wt./hr as a mixed vapor of water and MeOH, and the innerpressure of the reaction tank during the reaction was about 4 MPa.

The aqueous slurry of the obtained TA was sent to a cooling tank at aspeed of about 166 pts. wt./hr. The weight ratio of TA/water in thecooling tank was about 1/1. The TA/water slurry at about 250° C. wascooled down by a latent heat of vaporization of water due to flushing toatmospheric pressure, and the slurry was kept at about 100° C. Water inan amount equivalent to that vaporized during the cooling was fed to thecooling tank to keep the weight ratio of TA/water of the slurry in it atabout 1/1.

From the cooling tank, the TA/water slurry was sent to a solid-liquidseparator at a speed of 166 pts. wt./hr to obtain TA cakes. The weightratio of TA/water of the obtained water-containing TA cakes was about83:12. The water-containing cakes were sent to a slurry preparation tankin the next process in a wet state as it is.

In the obtained wet TA, the concentrations of DMT and MMT were 500 ppmand 50 ppm, respectively, and the total content of 4-CBA, p-TA and BAwas 30 ppm. Further, the 250° C. heat-resistant alkali permeability wasalso 99.9% or more, and the TA was suitable as a raw material of PET forbottles.

Subsequently, a slurry consisting of 45 pts. wt. of the TA cakes (40pts. wt. of TA and 5 pts. wt. of water) and 22 pts. wt. of EG wassupplied to a polycondensation tank, and esterification reaction wascarried out at 275° C. at atmospheric pressure for 4 hr. The byproducedwater and the TA-entraining water were allowed to flow outside thesystem, and the esterification reaction was carried out to 97% in theesterification reaction rate to prepare an oligomer having a degree ofpolymerization of 5 to 10. Subsequently, 0.017 pt. wt. of a trimethylphosphate solution in EG (5.5 mol % in terms of phosphorus atom) and0.38 pts. wt. of a germanium dioxide solution in EG (1.0 mol % in termsof germanium atom) were added to the oligomer, and polycondensation wascarried out for 1 hr under a reduced pressure of 2000 Pa andsuccessively for 2 hr under a reduced pressure of 133 Pa and at 277° C.

The produced polymer was taken out in a form of strand from an exitformed on the bottom of the polycondensation tank in such a state thatthe exit was directly linked to a cooling water tank. After cooled withwater in the tank, the strand was cut in chip-shape to obtain pellets.The obtained polymer pellets were crystallized in a stirringfluidized-type crystallizing machine followed by drying in nitrogen flowat 140° C. for 3 hr. Successively, they were transferred to a packedtower-type solid phase polymerizer and treated at 215° C. for 2 hr innitrogen flow for solid phase polymerization to produce a chip-shapedpolyethylene terephthalate resin.

The obtained chips had an intrinsic viscosity of 0.79, an AA content of3.0 ppm and an oligomer content of 0.3 ppm.

Subsequently, after dried at 160° C. for 5 hr in a vacuum drier, theobtained chips were subjected to an injection molding to obtain acylindrical preform by using an injection molding machine (M-100DMmanufactured by Meiki) at a cylinder temperature of 275° C., arotational speed of screw of 160 rpm, a primary pressure time of 3.0sec. a mold temperature of 10° C. and a cycle time of 30 sec. Thepreform had an outer diameter of about 28 mm, an inner diameter of about19 mm, a length of 136 mm and weight of about 56 g.

The obtained preform had an intrinsic viscosity of 0.68 and an AAcontent of 7.5 ppm, and it had excellent moldability and appearance.

Successively, after preheated by an infrared heater so that the surfacetemperature of the preform became about 110° C., the preform was treatedfor stretch blow molding by using a blow molding machine having setvalues of a blow pressure of 0.5 to 4.0 MPa and a mold temperature of150° C. to obtain a PET bottle having an average thickness at the bodyof 330 μm and an inner volume of about 1.5 litters. The obtained PETbottle had a haze of 0.6% and a high quality, and it was recognized thatthe present invention enables the recycling of used PET bottles again toPET bottles.

Example 2

The wet TA cakes having a weight ratio of TA/water of about 83:12obtained by cooling and solid-liquid separation after the hydrolysisreaction in Example 1 were charged into a nitrogen flow-type dryer at aspeed of 95 pts. wt./hr by gravity feeding to treat them for drying. Thewater content of the dried TA powder was 0.2 wt. %. The TA powder wassent to a TA storing tank.

In the obtained TA powder, the concentrations of DMT and MMT were 500ppm and 50 ppm, respectively, and the total content of 4-CBA, p-TA andBA was 30 ppm. Further, the 250° C. heat-resistant alkali permeabilitywas 99.8% or more, and the TA was suitable as a raw material of PET forbottles.

Subsequently, into a TA slurry tank was charged the TA at a speed of 83pts. wt./hr from the TA storing tank, and further EG at a speed of 50pts. wt./hr. They were stirred to produce a slurry. Subsequently, theTA/EG slurry was supplied from the TA slurry tank to an esterificationtank at a supply speed of 133 pts. wt./hr, and an esterificationreaction was carried out under stirring at 270° C. while distilling outEG and water under such a condition that the retention time became 2 hr.The distilled-out EG was used to the depolymerization reaction aftertreating by distillation together with the other EG generated in theprocesses of the present invention. The water was subjected to a wastewater treatment together with other generated water. The PET oligomerobtained in an esterification tank was supplied to an initialpolymerization tank at a speed of 102 pts. wt./hr, and at the same time,a Ge₂O₃ (germanium oxide) catalyst was supplied at a speed of 0.015 pt.wt./hr, and a polycondensation reaction was carried out in a weak vacuumof 2 kPa at 280° C. under stirring while removing EG by distillation.The distilled-out EG was partially recycled to the depolymerizationreaction after it was purified through a distillation treatment togetherwith other EG.

The PET oligomer was supplied from the initial polymerization tank to alatter-term polymerization tank at a supply speed of 97 pts. wt./hr, andin the latter-term polymerization tank, a polycondensation reaction wascurried out in a high vacuum of 0.13 kPa at 280° C. under stirring whiledistilling out EG to obtain a PET polymer. The intrinsic viscosity ofthe PET polymer was 0.51. The PET polymer was taken out from thelatter-term polymerization tank in a molten state, cooled in a coolingbath and subsequently cut by a cutter into pellets. The pellets weresupplied to a solid-phase polymerization tank at a supply speed of 96.5pts. wt./hr. The solid-phase polymerization tank was a packed-typepolymerizer furnished with a preliminary crystallizer. The solid phasepolymerization reaction was carried out in a vacuum of 0.65 kPa whilecontrolling a jacket temperature so that the temperature of the pelletsin the center of the tank was kept at 210° C. under such a conditionthat the retention time in the tank was about 8 hr. The obtained PETpolymer had an intrinsic viscosity of 0.76, a content of AA of 3.5 ppmand a content of oligomers of 0.3 ppm.

The PET polymer was the most suitable as a polymer for PET bottles.Further, the polymer was sent from the solid-phase polymerization tankto a PET storing tank at a speed of 96.4 pts. wt./hr to store it there.Subsequently, after dried for 5 hr at 160° C. in a vacuum dryer, theobtained chips were subjected to an injection molding to obtain acylindrical preform by using an injection molding machine (M-100DMmanufactured by Meiki) at a cylinder temperature of 275° C., arotational speed of screw of 160 rpm, a primary pressure time of 3.0sec, a mold temperature of 10° C. and a cycle time of 30 sec. Theobtained preform had an outer diameter of about 28 mm, an inner diameterof about 19 mm, a length of 136 mm and weight of about 56 g.

The preform had an intrinsic viscosity of 0.67 and an AA content of 12ppm, and it had excellent moldability and appearance.

Successively, after preheated by an infrared heater so that the surfacetemperature of the preform became about 110° C., the preform wassubjected to stretch blow molding to obtain PET bottles. The molding wasperformed by using a blow molding machine at set values of a blowpressure of 0.5 to 4.0 MPa and a mold temperature of 150° C. Theobtained PET bottle had an average thickness at the body of 330 μm andan inner volume of about 1.5 litters. The bottle had a haze of 0.5% anda high quality, and it was recognized that the present invention enablesthe recycling of used PET bottles again to PET bottles.

Reference Example 1

Except that the average size of crushed flakes in Example 1 was made 100mm by adjusting the aperture of the screen of the crusher, the operationconditions were same as in Example 1. Resultingly, the transportationefficiency in the pneumatic transportation of the crushed flakes waslowered, and the electric load of the blower for the transportation wasincreased. Further, when the depolymerization product of completedreaction was treated by a solid-liquid separator, the amount of solidsremained on the metal net was increased. The analysis of the compositionof the solids revealed that the amount increased from the solids inExample 1 was attributable to the PET of the unreacted product in thedepolymerization process. Accordingly, the recovery ratio of the productwas decreased.

Reference Example 2

After unpacking a bale of PET bottles, the PET bottles were charged intothe crusher, and they were crushed by using a screen whose aperture wasset at 10 mm as in Example 1. However, the crushed products were notsubjected to a winnower, not passed through the washing and gravitysorting process, that is, the contents of the bottles were not washedout with water, and foreign plastics were not removed by gravityseparation, and the flakes which had only been made small pieces wereused as the recovered PET flakes. Except this, Reference Example 2 wascarried out under same conditions as in Example 1.

The recovered DMT was analyzed in the same manner as in Example 1. Onthe analysis of organic impurities by gas chromatography, a number ofimpurities which could not be identified were detected. The chlorineconcentration in the DMT was 20 ppm, and the obtained DMT in thisreference example could not be referred to as a high-quality DMT.

Further, the 250° C. heat-resistant alkali permeability was poor, and itwas 93%.

Furthermore, the haze of the PET bottles manufactured by the same methodas in Example 1 was poorly 2.5%. When compared with Example 1, theintrinsic viscosity was largely lowered, there was the deterioration ofthe transparency, and totally the color tone was pale yellow. Thequality of the PET was so poor that the PET could not be used for PETbottles.

Reference Example 3

Except that the depolymerization reaction was carried out at atemperature of 220° C., the operation conditions were same as inExample 1. The recovered DMT was analyzed in the same manner as inExample 1, and the content of chlorine was 15 ppm, and a number ofimpurities which could not be identified were detected in the analysisof organic impurities by gas chromatography. Accordingly, the obtainedDMT in this reference example could not be referred to as a high-qualityDMT.

Further, the 250° C. heat-resistant alkali permeability was also poor,and it was 85%.

Furthermore, the haze of the PET bottles manufactured by the same methodas in Example 1 was 2.5%. When compared with Example 1, the intrinsicviscosity was largely lowered, there was the deterioration of thetransparency, and totally the color tone was pale yellow. The quality ofthe PET was so poor that the PET could not be used for PET bottles.

Reference Example 4

Except that after the completion of the ester interchange reaction, therecrystallization was not carried out, the operation conditions weresame as in Example 1. The recovered DMT was analyzed in the same manneras in Example 1, and the content of an isomer impurity consisting ofdimethyl isophthalate (DMI) was 800 ppm.

Successively, processes after hydrolysis were carried out in the samemanner as in Example 1 to obtain a preform having an intrinsic viscosityof 0.66. Further, blow moldering was carried out as in Example 1 toobtain bottles having a haze of 2.0%. Further, a crystallization speedduring the molding decreased, so that bottles having a sufficientstrength and heat stability could not be obtained.

Reference Example 5

Except that the DMT distillation was omitted in the process of DMTrecovery, the operation conditions were same as in Example 1. Therecovered DMT was analyzed in the same manner as in Example 1, and thecontent of chlorine was 5 ppm, and a number of impurities which couldnot be identified were detected by gas chromatography. Accordingly, theobtained DMT in this reference example was not referred to as ahigh-quality DMT. Further, slight nasty smell was detected in the DMT.

Further, the 250° C. heat-resistant alkali permeability of the TAobtained through hydrolysis was poor, and it was 90%.

Furthermore, the haze of the PET bottle manufactured by the same methodas in Example 1 was poorly 2.5%.

Reference Example 6

Except that the reaction temperature of the hydrolysis reaction was 180°C., the operation conditions were same as in Example 1. Resultingly, theconcentrations of MMT and DMT in the TA were 1300 ppm and 180 ppm,respectively.

By using the TA, the polymerization process was carried out in the samemanner as in Example 1, but the reactivity was low, so that it neededlonger time than usual to reach the objective intrinsic viscosity, andthe pellets were totally pale yellow. Their quality was so poor thatthey could not be used for PET bottles.

Reference Example 7

Except that the molar ratio of TA/EG in the slurry preparation tank was1:5, the operation conditions were same as in Example 1. Resultingly,the DEG content in the obtained pellets was high, and it was 4.3 wt. %.The pellets were totally pale yellow, and had extremely lowered heatresistance, and the pellets had such a poor quality that they could notbe used for PET bottles.

Industrial Field of Application

According to the present invention, a through process which comprisesobtaining a high-quality terephthalic acid from recovered used PETbottles via dimethyl terephthalate, and obtaining a PET polymer for PETbottles by using the terephthalic acid as a raw material, enables theeffective recycling of PET bottles, which receive special attention evenamong wastes due to their bulkiness and are becoming social issue.

1. A method for recycling PET bottles characterized in that the wastesof resin bottles containing polyethylene terephthalate (PET) as the maincomponent and further containing components different from it are passedsequentially through the following Processes (1) to (17): (1) a processfor unpacking a packed bale of PET bottles which have been recoveredthrough collection of classified refuse, (2) a process for removing ironand aluminum by a metal detector from the unpacked PET bottles, andsubsequently crushing the PET bottles into flakes of 2-30 mm in sizes,(3) a process for separating polymer components different from PET, oflabels (thin film) or the like and consisting of polyethylene (PE),polystyrene (PS), polyvinyl chloride (PVC) or the like from flaky piecesof PET bottles by winnowing, (4) a process for washing and gravitysorting having both the roles of washing out foreign materials attachedinside and outside the crushed PET bottle pieces and/or residues of thecontents inside the PET bottles with water, and further removing sands,stones etc. having specific gravities larger than water and PET, andforeign plastics such as PE and PP having specific gravity smaller thanwater, (5) a depolymerization process for producing bis-β-hydroxyethylterephthalate (BHET) by charging recovered PET flakes into EG containinga PET depolymerization catalyst and treating the mixture at atemperature of 175-190° C. under a pressure, of 0.1-0.5 MPa, (6) asolid-liquid separation process for removing solid foreign materialswhich have not dissolved in the above reaction solution, (7) a BHETconcentration process for distilling and concentrating the solutionfraction which has passed the solid-liquid separation process, (8) anester interchange-recrystallization process for forming crude DMT and EGthrough an ester interchange reaction of the concentrated BHET inmethanol (MeOH) in the presence of an ester interchange reactioncatalyst, and subjecting the reaction mixture to recrystallization in aMeOH solvent, (9) a DMT distillation process for removing MeOH bydistillation from the DMT cakes to purify the DMT, (10) a hydrolysisprocess for subjecting the purified DMT obtained in the DMT distillationprocess to a hydrolysis reaction together with water at a temperature of230-250° C. to produce TA, (11) a process for cooling an aqueous slurryof the TA obtained in the hydrolysis process, (12) a process forobtaining TA cakes from the cooled aqueous slurry of TA throughsolid-liquid separation, (13) a slurry adjusting process in which the TAcakes obtained in Process (12) are added to a slurry preparation tankafter they are dried, and the mole ratio of TA/EG is adjusted to 1:1 to1:3, (14) a process in which TA and EG are made to perform anesterification reaction to obtain a PET oligomer, (15) an initialmelt-polycondensation process in which a polycondensation catalyst and astabilizer are added to the PET oligomer, the mixture is subjected to amelt polycondensation reaction in a weak vacuum of 1.3 kPa to 4.0 kPa at260-300° C. to remove EG, and thus the degree of polymerization isincreased, (16) a latter term melt-polycondensation process in which theproduct of the previous process is further subjected to a meltpolycondensation in a high vacuum of 67 Pa to 0.7 kPa at 270-300° C. toremove EG by distillation, and thus the degree of polymerization isfurther increased, and (17) a solid phase polymerization process forincreasing the degree of polymerization in order to obtain a PETsuitable for bottles.
 2. A recycling method described in claim 1 inwhich the depolymerization catalyst to be used in Process (5) is atleast one kind of compound selected from a group consisting of carbonatesalts, hydrogencarbonate salts, hydroxides and alkoxides of an alkalimetal, carbonate salts, hydrogencarbonate salts, hydroxides andalkoxides of an alkaline earth metal, manganese acetate and zincacetate.
 3. A recycling method described in claim 1 in which thequantity of the addition of the depolymerization catalyst to be used inProcess (5) is 0.1 to 10 wt. % based on the weight of recovered PETflakes.
 4. A recycling method described in claim 1 in which the esterinterchange reaction catalyst to be used in Process (8) is at least onekind of compound selected from a group consisting of carbonate salts,hydrogencarbonate salts, hydroxides and alkoxides of an alkali metal,carbonate salts, hydrogencarbonate salts, hydroxides and alkoxides of analkaline earth metal, manganese acetate and zinc acetate.
 5. A recyclingmethod described in claim 1 in which the quantity of addition of theester interchange reaction catalyst to be used in Process (8) is 0,1 to10 wt. % based on the weight of the recovered PET flakes.
 6. A recyclingmethod described in claim 1 in which the TA cakes are mixed with EGwithout drying them in Process (13), and the mole ratio of EG/TA isadjusted to 1:1 to 1:3.
 7. A recycling method described in claim 1 inwhich the water content of the EG slurry in Process (13) is in the rangeof 0,1 to 20 wt. % based on the weight of EG.
 8. A recycling methoddescribed in claim 1 in which the TA to be supplied to Process (14) hasa rate of the total content of 4-carboxybenzaldehyde (4-CBA), methylparatoluate (p-TA), benzoic acid (BA) and dimethyl hydroxyterephthalateof 1 ppm or less, and a rate of the total content of monomethylterephthalate (MMT) and dimethyl terephthalate (DMT) in the range of 1to 5000 ppm.
 9. A recycling method described in claim 1 in which thepolycondensation reaction catalyst to be used in Process (15) is atleast one kind of compound selected from a group consisting of germaniumcompounds, antimony compounds and titanium compounds, and the stabilizerto be added is at least one kind of compound selected from phosphoricesters such as trimethyl phosphate, triethyl phosphate and triphenylphosphate, phosphorous esters such as triphenyl phosphite andtrisdodecyl phosphite, acidic phosphoric acid esters such as methyl acidphosphate, dibutyl phosphate and monobutyl phosphate, and phosphoruscompounds such as phosphoric acid, phosphorous acid, hypophosphorousacid and polyphosphoric acid.
 10. A recycling method described in claim1 in which the addition quantity of the polycondensation reactioncatalyst to be used in Process (15) is 0.002 to 0,1 wt. % of the weightof the TA supplied in Process (14).
 11. A recycling method described inclaim 9 in which the polycondensation reaction catalyst is amorphousgermanium dioxide, and the amount of the existence of the catalyst inthe reaction is 20 to 150 ppm in terms of germanium element based on theTA.
 12. A recycling method described in claim 9 in which thepolycondensation reaction catalyst is antimony trioxide, and the amountof the existence of the catalyst in the reaction is 100 to 400 ppm interms of antimony element based on the TA.
 13. A recycling methoddescribed in claim 9 in which the polycondensation reaction catalyst istitanium tetrabutoxide, and the amount of the existence of the catalystin the reaction is 1 to 100 ppm in terms of titanium element based onthe TA.
 14. A recycling method described in claim 9 in which thepolycondensation reaction catalyst is titanium trimellitate, and theamount of the existence of the catalyst in the reaction is 1 to 100 ppmin terms of titanium element based on the TA.
 15. A recycling methoddescribed in claim 9 in which the polycondensation reaction catalyst isa reaction product of titanium tetrabutoxide and mono-n-butyl phosphate,and the amount of the existence of the catalyst in the reaction is 1 to100 ppm in terms of titanium element based on the TA.
 16. A recyclingmethod described in claim 9 in which the polycondensation reactioncatalyst is a reaction product of titanium trimellitate and mono-n-butylphosphate, and the amount of the existence of the catalyst in thereaction is 1 to 100 ppm in terms of titanium element based on the TA.17. A recycling method described in claim 9 in which thepolycondensation reaction catalyst is a reaction product of titaniumtetrabutoxide and phenylphosphonic acid, and the amount of the existenceof the catalyst in the reaction is 1 to 100 ppm in terms of titaniumelement based on the TA.
 18. A recycling method described in claim 9 inwhich the polycondensation reaction catalyst is a reaction product oftitanium trimellitate and phenylphosphonic acid, and the amount of theexistence of the catalyst in the reaction is 1 to 100 ppm in terms oftitanium element based on the TA.
 19. A polyethylene terephthalateobtained by a recycling method described in claim 1, and having anintrinsic viscosity of 0.70 to 0.90, the content of an oligomer (cyclictrimer) of 0.50 wt. % or less and the content of acetaldehyde of 5 ppmor less.
 20. A molded product made of the polyethylene terephthalatedescribed in claim
 19. 21. A molded product described in claim 20 inwhich the molded product is a bottle-shaped article.
 22. A moldedproduct described in claim 20 in which the molded product is asheet-shaped article.
 23. A molded product described in claim 20 inwhich the molded product is a heat-molded container.
 24. A moldedproduct described in claim 20 in which the molded product is aninjection molded product.